Using The Night Sky in your Astronomy Classroom

The Night Sky is equally an observing aid for nighttime use and a miniature planetarium for use in the classroom. Use it for both purposes.

Why Observe the Sky in an Astronomy Class?

Astronomy without observation is like political science without geography. Students need a “conceptual link” between the dome of the sky available to their direct perception and the abstract universe of modern astronomy.

Students are generally eager to learn the sky: that may be why they signed up for the course. They are often disappointed with astronomy classes that are “all book and no look.”

Students who observe the sky come to their class work with a greater sense of anticipation and readiness to learn, and usually do better overall.

A Minimalist Strategy for Urban Skies or a Tight Schedule

Students who don’t recognize any star patterns do not have a sense of continuity from one night to the next, so they are unprepared to make even the simplest observations of celestial motions. Learning even a single star pattern makes the daily and seasonal motions of the sky apparent.

In summer/fall learn to find the Summer Triangle. In winter/spring learn to find Orion and the Winter Hexagon. These are all very bright star patterns and are visible in even the most light-polluted skies.

You might want to add to the list the bright polar asterisms (the Big Dipper and “W” of Cassiopeia with Polaris in between) when teaching about sky rotation.

You also might want to throw in the few remaining first magnitude stars (Arcturus, Spica, Regulus, Antares, and Fomalhaut, for the continental United States, plus a few more for Hawaii and South Florida). Once you know the first magnitude stars, the planets become conspicuous as bright stars “out of place.”

Why Learn the Constellations?

There are many answers to this question, but one pragmatic reason is to learn where to point a telescope or a pair of binoculars to see something fantastic! The Andromeda Galaxy is over four times the size of the full moon and easily visible in binoculars, but first you have to find it. For amateur observers the easiest way is to learn to find the constellation Andromeda (or use the western half of Cassiopeia as a pointer!). Numerous open and globular clusters and a handful of nebulae and galaxies are easily visible in binoculars…but you need the constellations as stepping stones.

First learn the brightest stars by name. Then learn the constellations containing those stars.
Always pay attention to the brightness of the stars as indicated by “dot size” on the chart so you will know what to look for. Try to find the brighter constellations first.
Review what you know each night, and gradually step your way around the sky from familiar constellations to neighboring constellations until you have learned the whole sky for the current season. Always learn new constellations in the context of their neighbors.
For faint constellations, learn bright constellations on either side, then “go between.” (For instance, the easiest way to find Hercules is to learn Bootes and Corona Borealis, on one side, then skip to Lyra. Then go half-way between Lyra and Corona Borealis to find the Keystone pattern in Hercules.)
Learn a few new constellations every month, or go out later at night if you don’t want to wait as long.
Don’t worry about seeing Cassiopeia as a queen or Auriga as a chariot driver. Face it: Cassiopeia looks like a distorted “W” and Auriga looks like a somewhat stretched pentagon. Constellations are random patterns of dots. Once you have identified the correct stars in a constellation ask yourself what they look like to you. The key question to ask is, would you recognize the pattern if you saw it again?

What to Observe in Urban Skies

Start with the minimalist strategy described above. Look for any “extra” stars that equal or exceed the brightness of the first magnitude stars? They are most likely planets.

How faint are the faintest stars visible from your location? Compare the faintest stars high in the sky areas closer to the horizon.

Use binoculars to trace out the constellations. Aiming binoculars at night will take some practice. Start by trying to point them at bright stars.

People often find they tend to aim low at first. Next practice tracing out constellations, starting with the most familiar ones. (You can probably only see one star of the Big Dipper at a time!)

As you get more familiar with the field of view of your binoculars, try tracing out progressively fainter constellations. How faint can you go?

Some of the “deep sky objects” plotted on The Night Sky are bright enough to be seen even in urban skies using binoculars. Try to find them.

The Night Sky as a Portable Planetarium

The Night Sky is as useful in the classroom as it is outside at night. It offers the benefit of hands-on learning while allowing students to accelerate time and even reverse time to learn about the movement of the stars across the night sky. It is also a more intuitive way to learn about the relationships and relative locations of the different constellations and how and why the sky changes over the course of the year.

Use the following questions to structure activities using The Night Sky as a portable planetarium:

What part of the sky never sets? What part of the sky never rises? (Hint: Look at the front and back sides of the chart as you turn the dial.) Express these two circular regions in terms of an angle measured outward from the two celestial poles for your latitude.

What is the angle from Polaris to the northern horizon at your latitude? Step 90° from the northern horizon to find the zenith point. (If you are using our plastic version, you can put a small dot at the zenith.) What is the angle from Zenith to the celestial equator at your latitude? …from the celestial equator to the southern horizon? What is the southernmost declination you can see from your latitude?
What direction does the sky move when you face north, south, east, west?
How much does the sky rotate from hour to hour? …from day to day? Express each of these as a fraction of a circle and/or an approximate angle in degrees.

Use The Night Sky to trace out the celestial equator. Look directly at the north celestial pole and tilt the chart so it is squarely in front of your eyes (perpendicular to an imaginary line from your eye, through the center eyelet of the chart, to the north celestial pole). Now, without changing the tilt, sight along the plane of the chart. This is the plane of the celestial equator. The front side of the chart maps the celestial hemisphere to the north of the equatorial plane, most of which is visible at any one time. The back side of the chart maps the celestial hemisphere to the south of the equatorial plane, most of which is below the horizon at any one time. This accounts for the asymmetry in the masking of the two sides of The Night Sky.

Use The Night Sky to teach about equatorial coordinates. Right Ascension is indicated along the celestial equator on either side of the chart at one hour intervals with meridians shown every three hours. Declination is marked along the meridians and labeled along every other meridian. For practice, students can locate stars at given coordinates or vice versa. A more useful application is to locate items on The Night Sky and use the coordinates to find them on an atlas (such as our Sky Atlas for Small Telescopes and Binoculars) or look them up in a catalogue.

Set the dial for today’s date and a reasonable observing time. Now advance the dial one hour. Is that enough motion to notice at night? Where in the sky would an hour’s rotation be most noticeable? Where would you look to see stars that are rising? Where would you look to see stars that are setting? How do the stars move near the north celestial pole? How do stars move near the southern horizon?

Locate the ecliptic on The Night Sky. The sun travels slowly along the ecliptic taking a year to make the complete circuit, moving a little less than 1° per day. Looking at the front side of the chart, find where the ecliptic is farthest north of the celestial equator. This is the summer solstice point: the location of the sun about June 20. Note that the meridian that passes through that point hits the outer date dial at about June 20. Note also that the sun on that day is about 23° north of the equator and moves, as the sky rotates, parallel to the equator throughout the day. Looking at the back of the chart, find where the ecliptic is farthest to the south of the celestial equator. That is where the sun would be about December 20, on the winter solstice.

Imagine the sun at the summer solstice point on June 20. Rotate the dial until the summer solstice point is on the eastern horizon. Look for the time corresponding to June 20 to find the time of sunrise. Now rotate the summer solstice point to the western horizon and find the time of sunset. Note that the sun on that date rises far to the north of east, moves high in the sky at midday (how far from zenith?), sets north of west, and stays above the horizon longer than 12 hours. Using the back of the chart locate the sunrise and sunset points, the duration of daylight, and the maximum elevation of the sun at the winter solstice. Repeat for the two equinoxes.

Companion Items

Our Exploring the Night Sky With Binoculars is especially useful as a short introduction to observational astronomy. It gives an overview of what objects can be seen and some basic descriptions of those objects.

Our Sky Atlas for Small Telescopes and Binoculars contains a useful introduction to the sky and plots and describes nearly 200 objects visible (in a dark sky) either in a pair of binoculars or a 60 mm telescope. As a classroom lab activity, items shown in the atlas can be located on The Night Sky to determine dates and times of visibility. They can also be the basis for internet searches for photographs and other descriptions.